Multiplexed Quantum Repeater

An elementary hyperlink of a quantum repeater based mostly on two absorptive QMs with the Sandwich-like construction. Credit score: WANG Guoyan and MA Yanbing

Chinese language researchers realized an elementary hyperlink of a quantum repeater based mostly on absorptive quantum reminiscences (QMs) and demonstrated the multiplexed quantum repeater for the primary time. On June 2nd, 2021, the work was printed in Nature.

The basic process of a quantum community is to distribute quantum entanglement between two distant places. Nevertheless, the transmission lack of optical fiber has restricted the space of entanglement distribution to roughly 100 km on the bottom. Quantum repeaters can overcome this problem by dividing long-distance transmission into a number of short-distance elementary hyperlinks. The entanglement of two finish nodes of every hyperlink is created firstly. Then the entanglement distance is steadily expanded by entanglement swapping between every hyperlink.

Beforehand, an elementary hyperlink of a quantum repeater has been realized in chilly atomic ensembles and single quantum programs. These demonstrations are all based mostly on emissive QMs, wherein the entangled photons are emitted from QMs. Quantum repeaters constructed by emissive QMs have easy constructions, however poor compatibilities. It’s of nice problem to help deterministic entanglement sources and multiplexed operations concurrently, that are two key applied sciences to boost the entanglement distribution price. Quantum repeaters based mostly on absorptive QMs can overcome such limitations as a result of they separate the quantum reminiscences and the entangled photon sources.

The analysis workforce, led by Prof. LI Chuanfeng and Prof. ZHOU Zongquan from College of Science and Expertise of China (USTC), focuses on the analysis of absorptive QMs based mostly on rare-earth-ion-doped crystals. For this sort of QMs, the entanglement supply will be flexibly chosen, together with deterministic entanglement sources, whereas remaining the potential of multiplexed operations, and subsequently must be extra environment friendly for quantum repeater functions. On this work, they used exterior entangled photon-pair sources (EPPSs) based mostly on spontaneous parametric down-conversion and achieved heralded entanglement distribution between two absorptive QMs for the primary time.

They constructed an elementary hyperlink with an intermediate station and two nodes on the ends. Every node incorporates an absorptive QM with a bandwidth of 1GHz and a bandwidth-matched EPPS. In every node, one entangled photon of every photon pair was saved within the “Sandwich-like” QM whereas the opposite was transmitted to the center station for joint Bell-state measurement (BSM). A profitable entanglement swapping operation was heralded by the profitable click on of BSM. The entanglement between two QMs 3.5 meters aside was established with a constancy of roughly 80.4%, though there weren’t any direct interactions between two distant QMs. 4 temporal modes had been employed on this demonstration of an elementary hyperlink of a quantum repeater, accelerating the entanglement distribution price by 4 occasions.

Prof. ZHOU Zongquan mentioned: “Using absorptive quantum reminiscence is predicted to realize excessive effectivity quantum repeater and quantum community sooner or later, and additional promote the communication between ‘Cowherd and Weaver Lady’ within the quantum world.”

This work supplies a possible roadmap for the event of sensible quantum repeaters and lays the inspiration for the development of high-speed quantum networks. Reviewers identified”The current work focuses on the ensemble strategy, which has an a variety of benefits within the context of quantum repeater functions, multiplexing as an illustration.” They extremely advocate this work as”a big accomplishment that can type the idea for additional analysis” and “a serious step ahead within the growth of a sensible quantum repeater.”

Prof. LI Chuanfeng mentioned that the workforce will proceed to enhance the symptoms of absorptive QM, “we’ll use deterministic entanglement supply to drastically enhance the entanglement distribution price, and to realize sensible quantum repeaters past direct transmission of optical fiber.”

For future developments, the analysis workforce will proceed to enhance the performances of the absorptive QMs, and undertake deterministic entanglement sources, in order to drastically improve the entanglement distribution price, and to realize a sensible quantum repeater that outperforms the direct transmission of photons.

Reference: “Heralded entanglement distribution between two absorptive quantum reminiscences” by Xiao Liu, Jun Hu, Zong-Feng Li, Xue Li, Pei-Yun Li, Peng-Jun Liang, Zong-Quan Zhou, Chuan-Feng Li and Guang-Can Guo, 2 June 2021, Nature.
DOI: 10.1038/s41586-021-03505-3

LIU Xiao and HU Jun from CAS Key Laboratory of Quantum Info and CAS Heart for Excellence in Quantum Info and Quantum Physics are the co-first authors. The corresponding authors are Prof. LI Chuanfeng and Prof. ZHOU Zongquan.

By Rana

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